Device for the Continuous Electrochemical Deionisation with Integrated Membrane Unit

ABSTRACT

A device for the electrodeionisation of an aqueous electrolyte solution, comprising an electrodeionisation module ( 1 ), an ultrafiltration module ( 21, 22, 1201, 1202, 1203 ) and a connection piece ( 3, 10 ) which connects the electrodeionisation module ( 1 ) and the ultrafiltration module ( 21, 22, 1201, 1202, 1203 ) such as to be able to guide a diluate produced from said electrolyte solution during operation of said device in said electrodeionisation module ( 1 ) from said electrodeionisation module ( 1 ) to said ultrafiltration module ( 21, 22, 1201, 1202, 1203 ); wherein said connection piece ( 3, 10 ) comprises no adjustable pressure-maintaining valve. By means of the pressure drop occurring in the ultrafiltration modules ( 21, 22, 1201, 1202, 1203 ) these devices build up a counter pressure behind the electrodeionisation module ( 1 ) which is sufficient to ensure the packing density of the ion exchanger in the electrodeionisation module ( 1 ).

FIELD OF THE INVENTION

The invention relates to a new device for the continuous electrochemicaldesalination and filtration of aqueous solutions which s in the form ofa spiral wound module.

PRIOR ART

The method of electrodeionisation per se has been known since the late1950s. A description of the method was first given in Industrial andEngineering Chemistry 1955, Vol. 47, No. 1. Devices for performing themethod in plate modules are described, for example, in U.S. Pat. No.4,465,573 and U.S. Pat. No. 4,925,541.

Spiral wound modules for electrodeionisation, in which both the aqueouselectrolyte solution to be desalinated and the concentrate are guidedtangentially (i.e. from the outer casing surface spirally towards theinside to the centre or vice versa) are described for instance in EP-A-0570 341.

Spiral wound modules for electrodeionisation, in which the concentrateis guided tangentially but the electrolyte to be desalinated is guidedaxially (i.e. from one front side of the module to the other front side)are described in WO-A-2004/101119 and in U.S. Pat. No. 6,190,528.

In all of the cited embodiments a continuous electrochemicaldesalination is described, in which cation and anion exchange membranesare arranged alternatingly between two electrodes, cathode and anode.The space between two adjacent membranes each defines a dilution chamberor a concentrate chamber, respectively. The dilution chamber is filledwith either ion exchange resin and/or ion conductive material to definethe chamber geometry. The concentrate chamber is formed from a mesh ofplastic (spacer) and/or ion conductive material (e.g. ion exchangeresin). The number of dilution and concentrate chambers can vary from arepeating unit to a plurality (technically designed max. 36). Therespective designed possibilities to seal individual chambers againstthe outside can be seen in the quoted specifications.

In operation of the modules the dilution chamber or dilution chambersare passed through in a single passage, while the concentrate side canbe passed through in a single or repeated passage depending on the modeof operation. The distribution of the inflowing water in the module ontothe individual chambers is achieved via internal distribution systems.

When the dilution chamber is flowed through under pressure the water tobe treated is guided over the ion exchanger resin. Depending on theoperating conditions wear debris and fine particles may be generated dueto the mechanical stress through the pressure drop over the ion exchangeresin. Usually, the influx and efflux openings of the individualchambers are shaped such that no ion exchanger grain and no biggerfragments of the ion exchanger grain can be flushed out of the chambers.This can be effected e.g. by introducing a resin safety mesh. Theseparation limit of the mesh is at around 200 μm. Smaller particles maypass through the mesh and thus reach the subsequent process stages ofthe water treatment, together with the product water. Microorganisms,usually having a size of between 0.2 and 5 μm, from process stagesupstream of the electrodeionisation module may also be regarded asparticles, since the process of water treatment, e.g. for thepharmaceutical, microelectronic, or power plant industry, is, from aneconomic point of view, not carried out under sterile conditions. Thus,in order to protect subsequent process stages against particles, amembrane module, such as an ultrafiltration module, is often connectedin series downstream of the electrodeionisation module.

On the other hand, it has been shown that in operation of modules forelectrodeionisation as described above, the packing density of the ionexchange resin in the dilution chamber has a favorable effect on theachievable quality (residual conductivity) of the product water. Thepacking density of the ion exchanger can in turn be influenced via theinternal pressure (not the pressure drop) in the electrodeionisationmodule. Until now, to achieve a certain internal pressure an adjustablepressure-maintaining valve was provided downstream of theelectrodeionisation module but upstream of the membrane module, wherebyan appropriate counter pressure was applied to the product water side(diluate) of the electrodeionisation module. For spiral wound moduleswhere the flow of the electrolyte is guided tangentially, this counterpressure was typically selected between about 0.5 and 1 bars; for spiralwound modules where the flow of the electrolyte is guided axially, thiscounter pressure was typically selected at around 0.3 to 3 bars.

It is an object of the invention to provide a device and a process inwhich the required counter pressure on the diluate side of theelectrodeionisation module can be achieved during its operation, whilesimultaneously the separation of particles, wear debris of the ionexchange resin and/or of microorganisms can be achieved.

SUMMARY OF THE INVENTION

The object is solved according to the invention by a device for theelectrodeionisation of an aqueous electrolyte solution, comprising anelectrodeionisation module, an ultrafiltration module and a connectionpiece which connects the electrodeionisation module and theultrafiltration module such as to be able to guide a diluate producedfrom said electrolyte solution during operation of said device in saidelectrodeionisation module from said electrodeionisation module to saidultrafiltration module; wherein said connection piece comprises noadjustable pressure-maintaining valve.

Preferred embodiments of the device according to the invention arisefrom the dependent claims.

DETAILED DESCRIPTION OF THE INVENTION

Surprisingly, it was found that an ultrafiltration module, which issituated downstream of the electrodeionisation module, is not onlysuitable for separating ion exchanger residues and bacteria from thediluate but also simultaneously serves for producing the counterpressure behind the electrodeionisation module, which is important formaintaining the packing density of the ion exchanger in theelectrodeionisation module. This is also surprising because theultrafiltration modules do not produce a constant, predictable counterpressure; in the course of their operation they gradually become cloggedwith filter residues and thus produce behind the electrodeionisationmodule a counter pressure increasing in time. Using the ultrafiltrationmodules as counter pressure producing means obviates the need to installa pressure-maintaining valve in or downstream of the electrodeionisationmodule, or upstream of or in the ultrafiltration module.

Within the scope of the present application “electrodeionisation module”is understood as any electrochemical cell, comprising:

a) an electrolyte solution-filled or electrolyte solution-flowed throughcathode compartment having a cathode and a cation exchanger membrane,the cation exchanger membrane forming one of the spatial limitations ofthe cathode compartment, and wherein the electrolyte solution(=catholyte) which fills or flows through the cathode compartmentcontacts the cathode and the cation exchanger membrane;

b) an electrolyte solution-filled or electrolyte solution-flowed throughanode compartment having an anode and an anion exchanger membrane, theanion exchanger membrane forming one of the spatial limitations of theanode compartment, and wherein the electrolyte solution (=anolyte) whichfills or flows through the anode compartment contacts the anode and theanion exchanger membrane; and

c) an intermediate compartment, said cation exchanger membrane and saidanion exchanger membrane forming two of the spatial limitations of thisintermediate compartment. Optionally the intermediate compartment may besubdivided into subcompartments by further cation and anion exchangermembranes located therein in pairs and arranged spaced apart from eachother. All cation and anion exchanger membranes which limit andoptionally subdivide the intermediate compartment are arranged inalternating order, when viewed along the gradient of the electricalfield. If viewed from the cathode towards the anode along the gradientof the electrical field, then each of the subcompartments enclosed by acation exchanger membrane/anion exchanger membrane pair is filled withan ion exchange resin, preferably a mixed bed ion exchange resin, orwith an ion conductive material, and is flowed through by theelectrolyte solution to be desalinated (=“diluate chambers”), while eachsubcompartment enclosed by an anion exchanger membrane/cation exchangermembrane pair is flowed through by the electrolyte solution to beconcentrated “concentrate chambers”). The electrolyte solution presentin the cathode compartment a) and the anode compartment b) is alsoconcentrated with electrolytes during the electrochemical operation,hence they are also “concentrate chambers”. The electrolyte solution ina diluate chamber contacts both ion exchanger membranes limiting thediluate chamber and is separated from the electrolyte solution of anadjacent concentrate chamber by at least one such ion exchangermembrane.

Preferred examples of electrodeionisation modules that can be usedaccording to the invention are the plate modules and spiral woundmodules mentioned above. In plate modules the concentrate and diluatechambers are all passed through in parallel flow without beinginterconnected. In a spiral wound module the outlet of each concentratechamber (viewed in the direction of the gradient of the electricalfield) is directly connected to the inlet of a next concentrate chamber(i.e. the cation exchanger or anion exchanger membrane, respectively, ofone concentrate chamber is seamlessly connected with the cationexchanger or anion exchanger membrane, respectively, of the nextconcentrate chamber), and inlets and outlets for the concentrate areonly provided in the anode compartment b) and in the cathode compartmenta). Likewise, the outlet of a diluate chamber is directly connected withthe inlet of a next diluate chamber (viewed in the direction of thegradient of the electrical field), and an inlet for the electrolytesolution to be desalinated is provided only in the one outermost diluatechamber and the outlet for the diluate only in the other oppositeoutermost diluate chamber.

More preferred are spiral wound modules, and particularly preferred arespiral wound modules wherein the flow directions in the concentratechambers on the one hand and the aqueous electrolyte solution to bedesalinated in the diluate chambers on the other hand overcross eachother; and whereby the flow direction in the diluate chambers runs inparallel to the winding axis of the spiral wound module, i.e. axially.

Within the scope of the present application “ultrafiltration module” isunderstood as any filter capable of removing microorganisms byfiltration from an aqueous solution. For this, ultrafiltration modulestypically contain at least one semipermeable membrane made of a polymerhaving an adequate pore size. Examples of such polymers are for instancepolyolefins such as polyethylene, polypropylene orpoly(4-methylpentene-1); polysulphones; polyethersulphones; aromaticpolyamides; polyimides; polyamides-imides; or fluorine-containingpolymers such as polyvinylidene fluoride, polytetrafluoro-propylene,copolymers of hexafluoropropylene, and tetrafluoropropylene. Theexclusion limit of the membrane is typically in the range of 5000 to400000 daltons. An ultrafiltration module to be used according to theinvention preferably contains the semipermeable membrane in the form ofa plurality of hollow fibers. For membranes in the form of hollow fiberspolyvinylidene fluoride and polyether sulphones are preferred aspolymers. The hollow fibers preferably have a pore width of about 0.01to about 0.2 μm, more preferably of about 0.05 to about 0.2 μm. Theypreferably have an inner diameter of about 10 to about 200 μm, morepreferably of about 50 to about 150 μm. The total membrane surface,which is formed in such an ultrafiltration module by all hollow fibers,is preferably about 0.01 to about 3 m², more preferably about 0.05 toabout 1.5 m². The manufacture of hollow fibers with the abovementioneddesired characteristics has been known per se for a long time; referenceis made by example only to the paragraph “Hollow Fiber Membranes” in“Kirk-Othmer Encyclopedia of Chemical Technology”, 3^(rd) edition, JohnWiley & Sons 12:492-517 (1984). Ultrafiltration modules with hollowfibers of the above-described type are known from the household, such asfilters in water taps (see e.g. WO-A-02/076589 or U.S. Pat. No.5,045,198).

The aqueous solution to be filtered is guided into the ultrafiltrationmodule via an inlet opening and can either enter from the outer space ofthe hollow fibers into their lumen, or exit from the lumen of the hollowfiber into the outer space; the former is preferred. The hollow fiberscan run in the longitudinal direction in the ultrafiltration module(such as parallel to a longitudinal axis of the ultrafiltration module),such that they therein form a straight bundle. Preferably, however, thehollow fibers are bent into a U-shape inside the ultrafiltration moduleand point with their open ends towards the filtrate side of theultrafiltration module. The diluate to be filtered, coming from theelectrodeionisation module, is guided into the interior of theultrafiltration module and enters the hollow fibers, as mentioned aboveas preferable. Since both ends of each hollow fiber point to thefiltrate side of the ultrafiltration module both ends form an outlet forthe filtrate. The filtrate exiting the hollow fibers can be removed fromthe ultrafiltration module via an adequate outlet opening which ishydraulically connected to the ends of the hollow fibers.

As the “connection piece connecting the electrodeionisation module andthe ultrafiltration module such as to be able to guide the diluateproduced from the electrolyte solution in said electrodeionisationmodule during the operation of said device from said electrodeionisationmodule to said ultrafiltration module” is understood any assembly partthat can carry out such a function. Examples of these are pipes,conduits, tubes or connecting pieces; or also a mounting or bracket partfor the electrodeionisation module and/or the ultrafiltration module(s)which simultaneously has means for guiding the diluate (such as inneropenings or channels). Such a mounting or bracket part may preferablyalso comprise a collection system which collects the diluate exitingfrom a plurality of outlet openings of the electrodeionisation moduleand transfers it in one single conduit to the ultrafiltration module; itmay also contain a distribution system, which evenly distributes thediluate coming from the electrodeionisation module to a plurality ofultrafiltration units connected in parallel.

Within the present application “adjustable pressure-maintaining valve”is understood as a valve whose interior pressure drop can be variablyadjusted. The device according to the invention does not comprise such apressure-maintaining valve in the connection piece, and preferably it isalso devoid of such a pressure-maintaining valve inside theelectrodeionisation module and also inside the ultrafiltration module.If the device according to the invention has a plurality ofultrafiltration modules and correspondingly possibly a plurality ofconnection pieces connecting the electrodeionisation module and each ofthese ultrafiltration modules, then none of these connection pieces andnone of the ultrafiltration modules contain such a valve.

Within the present application two cavities or recesses (collectionspaces, channels, bores, recesses, distribution spaces or openings) are“hydraulically connected” if they allow the passage of liquid from onecavity to the other cavity without leaking that liquid and withoutappreciable pressure drop.

The manufacture of the device according to the invention is according tothe art since the used electrodeionisation modules and ultrafiltrationmodules are known per se. The hydraulic connection of theabove-described connecting piece with the ultrafiltration modules andwith the collection system of the spiral wound module may be carried outby glueing, welding or by a screw tube fitting, depending on the pair ofmaterials involved.

A further possibility of connecting the ultrafiltration modules with theconnecting piece in an outer housing pipe is by using one or moretie-rods. The ultrafiltration modules in the corresponding openings ofthe connecting element are sealed by elastomer seals. The flow guidancein the device according to the invention thus results from a connectionon the influx side, an optional integrated distribution system in theconnecting piece (which distributes the diluate onto the ultrafiltrationmodules), the flowing in parallel through the individual ultrafiltrationmodules, and an optional integrated collection system in an optionalfilter holding plate (which collects the filtrate exiting from theultrafiltration modules). The correct spacing between the connectingpiece and the filter holding plate may be achieved, if desired, by rodsor distance supports. The remaining clearance in the combination ofconnecting piece/ultrafiltration units/filter holding plates/optionaldistance supports is not flowed through and is designed as an air space.

The individual ultrafiltration modules are typically flowed through at avolume flow of 100 1/h to 600 1/h, preferably of 250 to 400 1/h. Thenumber of ultrafiltration modules to be incorporated therefore resultsfrom the integral quotient of the nominal volume flow of theelectrodeionisation module and the preferred volume flow of eachultrafiltration module (i.e. for e.g. 500 1/h 2 pieces and for 10001/hat least 3 pieces).

Hydraulically connecting the above-described connecting element and thefilter holding plate with the ultrafiltration units and the collectionsystem of the electrodeionisation module can be performed with a sealring having an integrated O-ring seal. For the technical implementationof the device the electrodeionisation module is preferably surrounded bya reinforced plastic casing or a steel or stainless steel pipe.

For the technical implementation the device according to the invention,comprising (or particularly consisting of) an electrodeionisationmodule, ultrafiltration modules, the connecting piece and a filterholding plate, is surrounded by a reinforced plastic casing or a steelor stainless steel pipe having a fixed flange. The connection of theelectrodeionisation module and the device is done by screwing the flangelid and the fixed flange together.

The devices according to the invention are suitable for theelectrodeionisation of raw waters usually employed for this purpose.These are, for example, natural raw waters, tap water or sea water.These all contain certain proportions of dissolved salts, dissociated inions and are therefore all electrolytes. Preferably, the raw water ispreviously partly desalinated and/or softened, such as by an upstreamreverse osmosis step. The raw water, i.e. the electrolyte to bedesalinated, may also previously have been subjected to a germicidaltreatment, for instance through UV radiation, a treatment with ozone,chlorine or hypochlorite; it may also have been subjected beforehand tofiltration for removing airborne particles and/or microorganisms.

DESCRIPTION OF THE FIGURES

The invention will now be further illustrated with reference to thedrawings, in which:

FIG. 1 is a sectional view of a first embodiment of the device accordingto the invention, showing at the top again the connecting piece usedtherein in a plan view;

FIG. 2 is a sectional view of a second embodiment of the deviceaccording to the invention, showing at the bottom left again theconnecting piece used therein in a plan view;

FIGS. 3 and 4, respectively, show the results of comparative testsconcerning the formation and quality of the diluate in a prior artdevice and the device according to embodiment 1, respectively.

EMBODIMENT 1 (FIG. 1)

In this embodiment a spiral wound module is employed aselectrodeionisation module 1, in which the electrolyte solution to bedesalinated and the concentrate are guided tangentially through thespirally wound diluate and concentrate chambers. It is designed for anominal capacity of typically about 400 to about 700 1/h of electrolytesolution to be deionised. The hydraulic and electrical connections ofthe spiral wound module are not shown here. This embodiment has twoultrafiltration modules 21, 22 (hollow fiber membrane filters). They arecommercially available legionella filters fitted with hollow fibermembranes having an exclusion limit of about 100000 daltons. The hollowfibers are bent in a U-shape (see preceding general description). Thetwo ultrafiltration units are held on their sides facing the spiralwound module by a connecting piece 3. On the filtrate side of the twoultrafiltration units 21, 22 these are held by a filter holding plate 4.Connecting piece 3 and filter holding plate 4 are located in an outerhousing pipe 5 made of steel, stainless steel or plastic. The connectingpiece 3 (shown again in the upper part of the Figure in a plan view,seen from the ultrafiltration modules 21, 22) has an opening 6, whichguides the diluate from the spiral wound module to the twoultrafiltration units 21, 22. Running inside the connecting piece 3 is achannel 7, hydraulically connecting the sockets 211, 221 of the twoultrafiltration units 21, 22 and thus forming a distribution systemwhich distributes the diluate passing through opening 6 onto the twoultrafiltration units 21, 22. Also, between connecting piece 3 andfilter holding plate 4 two distance supports 81, 82 made of chromiumsteel are present. The combination of connecting piece 3,ultrafiltration units 21, 22, filter holding plate 4, housing pipe 5 anddistance supports 81, 82 is cut along section plane A-A′ in FIG. 1; thelocation of which is indicated in connecting piece 3 shown again above.Due to the location of section plane A-A′ only one ultrafiltrationmodule 22 and only one distance support 81 is visible in FIG. 1; forthis reason channel 7 is not visible in this sectional view. Inconnecting piece 3 bores 211, 221 are provided for accommodating theultrafiltration modules; also, in filter plate 4 corresponding bores(only one with reference numeral 222 being visible) are contained. Theultrafiltration modules 21, 22 may be fixedly connected in theindividual bores 211, 221, 222 with the connecting piece 3 and thefilter plate 4 through bonding or welding or by means of seal rings. Theflow of the diluate exiting the spiral wound module occurs throughopening 6, through said distribution system in the connecting element 3,through the two ultrafiltration modules 21, 22 in parallel connectionand then, optionally, through a corresponding collection system (notshown in the Figure), incorporated into the filter holding plate, andthen via an also optional adapter, which is not shown in the Figure. Thespace between connecting piece 3 and filter holding plate 4 outsideultrafiltration modules 21, 22 and housing pipe 5 is not flowed throughand is designed as an air space. The inlets and outlets for theconcentrate, the influxes for the electrolyte solution to be desalinatedand the electrical connections are not shown in the Figure; they wouldbe present outside the housing pipe 5 on the front side of the device.The entire device according to embodiment 1 can be incorporated in apreferably cylindrical casing element 9.

EMBODIMENT 2 (FIG. 2)

This embodiment of the device according to the invention is designed fora nominal capacity of typically about 2500 to about 3300 1/h ofelectrolyte solution to be deionised. It contains as theelectrodeionisation module 1 a spiral wound module, wherein the diluateand concentrate are guided in cross-flow (with the diluate being guidedaxially). “P” indicates the axial influxes of the electrolyte solutionto be desalinated (“P” stands for permeate, since the electrolyte beingsupplied is preferably already the permeate of an partially desalinatingreverse osmosis being located upstream). “D” indicates the axialeffluxes of the diluate. “Ci” denotes the inlet for the concentrate(Concentrate inlet) and “Co” denotes the outlet for the concentrate(Concentrate outlet). The two connections for the direct current arealso indicated with “+” and “−”. The diluate outlets D of theelectrodeionisation module 1 lead into a connecting piece 10 (forinstance made of a polyoxymethylene copolymer) having a collection space11 and nine openings for the diluate exiting the electrodeionisationmodule 1 (only one of these is shown with reference numeral 101). Eachof the nine openings is drilled and shaped such that one ultrafiltrationmodule can be inserted in each of them using one seal ring each (forinstance made of EPDM rubber or NBR). The nine ultrafiltration modulesin total (only three of these are shown with reference numerals 1201,1202, 1203) are commercially available legionella filters, fitted withhollow fiber membranes having an exclusion limit of 100000 daltons. Thehollow fibers are bent in a U-shape (see preceding general description).The nominal maximum passage volume of each ultrafiltration module 1201,1202, 1203 is about 800 1/h. The nine ultrafiltration modules are fittedbetween connecting piece 10 and a filter holding plate 14 with the aidof six distance supports made of chromium steel (only one of these isshown with reference numeral 13). The filter plate 14 in turn has nineopenings for the filtered permeate (only one of these is shown withreference numeral 15), the ultrafiltration modules being fitted thereinby means of seal rings made of EPDM rubber, silicone rubber or NBR. Thefilter holding plate 14 also has a collection space 16 on its outer sidefor the filtered diluate. This collection space 16 is shut off through ascrewed on flange lid 17 with a central outlet connection 18. Thecombination of connecting piece 10, the nine ultrafiltration modules,the six distance supports and the filter holding plates 14 is shown cutoff in the Figure. The connecting piece 10 is shown again in the Figureat the bottom left in a plan view, seem from the ultrafiltrationmodules; here the location of the section plane A-A′ is indicated, inwhich said combination is shown cut off. Here the arrangement of allnine ultrafiltration modules is visible: six of them are arranged in acircular arrangement outside on the connecting piece, the remainingthree are arranged in the centre of the connecting piece. The sixdistance supports are also shown here (only one of the supports, whichis visible cut off in the sectional view is indicated again by referencenumeral 13). The dotted circle 11 indicates the collection space for thediluate exiting the electrodeionisation module 1; the dots indicate thatthe collection space is on the back of the connecting element 10.

Comparative Test (FIGS. 3 and 4)

On the one hand a conventional device for electrodeionisation,comprising a spiral wound module according to EP-A-0 570 341 and adownstream-sitauted pressure-maintaining valve, and on the other hand andevice according to the invention according to embodiment 1 notcontaining a pressure-maintaining valve, were compared with each otherin a long-term test regarding the operating parameters, particularlyregarding the counter pressure occurring behind the spiral wound module,and regarding the rate of production and the residual conductivity ofthe diluate formed in the spiral wound module. The results are shown inFIGS. 3 and 4. In these Figures:

● is the residual conductivity of the diluate (in μS/cm);

— is the counter pressure in the diluate, thus behind the spiral woundmodule (in bar);

Δ is the rate of production of diluate (in 1/h);

♦ is the pressure in the reverse osmosis permeate fed to the spiralwound module (in bar); and

▪ is the residual conductivity in the reverse osmosis permeate fed tothe spiral wound module (in μS/cm).

In the conventional device water from a reverse osmosis was fed to thespiral wound module under pressure. On the diluate side (pure water) ofthe module a counter pressure of approx. 1 bar was set by means of thepressure-maintaining valve. By applying a typical potential to theelectrodes of the spiral wound module diluate was produced during 192hours. The measured operating parameters are illustrated in FIG. 3. Ascan be seen from FIG. 3, a constant water quality of 0.058 μS/cm at arate of production of 1000 1/h was achieved.

The device according to embodiment 1 was also fed with permeate from areverse osmosis. On the diluate side (i.e. behind the spiral woundmodule) of the device the counter pressure was produced solely by thetwo ultrafiltration modules 21, 22 downstream, since nopressure-maintaining valve was present here. By applying a typicalpotential to the electrodes of the spiral wound module diluate wasproduced during 288 hours. The measured operating parameters areillustrated in FIG. 4. As can be seen from FIG. 4 a constant waterquality of 0.055-0.056 μS/cm at a volume flow of 1000 1/h was alsoachieved.

1. A device for the electrodeionisation of an aqueous electrolytesolution, comprising an electrodeionisation module (1), anultrafiltration module (21, 22, 1201, 1202, 1203) and a connection piece(3, 10) which connects the electrodeionisation module (1) and theultrafiltration module (21, 22, 1201, 1202, 1203) such as to be able toguide a diluate produced from said electrolyte solution during operationof said device in said electrodeionisation module (1) from saidelectrodeionisation module (1) to said ultrafiltration module (21, 22,1201, 1202, 1203); wherein said connection piece (3, 10) comprises noadjustable pressure-maintaining valve.
 2. The device according to claim1, which does not comprise an adjustable pressure-maintaining valve inthe electrodeionisation module (1) and in the ultrafiltration module(21, 22, 1201, 1202, 1203).
 3. The device according to claim 1 or 2,wherein the electrodeionisation module (1) is a spiral wound module. 4.The device according to claim 3, wherein the flow of the electrolytesolution to be desalinated is guided axially in said spiral woundmodule.
 5. The device according to claim 1, wherein the ultrafiltrationmodule (21, 22, 1201, 1202, 1203) comprises filter membranes in the formof hollow fibers.
 6. The device according to claim 5, wherein the hollowfibers inside the ultrafiltration module (21, 22, 1201, 1202, 1203) arebent in a U-shape, such that both bent ends of each hollow fiber arehydraulically connected with an outlet opening of the ultrafiltrationmodule (21, 22, 1201, 1202, 1203); whereby the diluate from theelectrodeionisation module (1) is filtered at the hollow fibers byentering a lumen of the hollow fibers from an outer space of the hollowfibers.
 7. The device according to claim 1, comprising a plurality ofultrafiltration modules (21, 22, 1201, 1202, 1203) connected inparallel.
 8. The device according to claim 1, which is incorporated intoa casing element (9).
 9. The device according to claim 1, comprising: a)an electrodeionisation module (1) in the form of a spiral wound module,in which flows in the concentrate chamber(s) and in the diluatechamber(s) are guided in parallel and tangentially, b) one to tenultrafiltration modules (21, 22), each of the ultrafiltration modules(21, 22) comprising in its interior hollow fibers bent in a U-shapehaving open ends, the bent open ends being hydraulically connected withan outlet opening of the ultrafiltration module (21, 22); and c) aconnecting piece (3) with a first side and a second side, wherein on itsfirst side is attached said spiral wound module (1) and on its secondside is attached said ultrafiltration module(s) (21, 22), which has anopening (6) and an inner channel (7) both being hydraulically connectedto each other, and each ultrafiltration module (21, 22) being attachedto the connecting piece (3) such that its inlet opening for the diluateis hydraulically connected with the channel (7).
 10. The deviceaccording to claim 1, comprising: a) an electrodeionisation module (1)in the form of a spiral wound module, in which flows are guidedtangentially in the concentrate chamber(s) and axially in the diluatechamber(s), b) one to fifteen ultrafiltration modules (1201, 1202,1203), each of the ultrafiltration modules (1201, 1202, 1203) comprisingin its interior hollow fibers bent in a U-shape and having open ends,said bent open ends being hydraulically connected with an outlet openingof the ultrafiltration module(s) (1201, 1202, 1203); and c) a connectingpiece (10) with a first side and a second side, wherein on its firstside is attached said spiral wound module (1) and on its second side areattached said ultrafiltration modules (1201, 1202, 1203), and having onits first side a collection space (11), which is able to collect thediluate produced in operation of the device in the electrodeionisationmodule (1) from the electrolyte solution, and having on its second sidea number of openings (101) hydraulically connected to the collectionspace (11), whereby said number of openings (101) is equal to the numberof ultrafiltration modules (1201, 1202, 1203), and each ultrafiltrationmodule (1201, 1202, 1203) is attached to said connecting piece (10),such that its inlet opening for the diluate is hydraulically connectedto the opening (101).
 11. A method for electrodeionisation of an aqueouselectrolyte solution, whereby a device according to claim 1, 9 or 10 isemployed.